1. Field of the Invention
This invention relates to a process for producing superconducting ceramics material, and more particularly to a method of producing superconducting ceramic in which a simple mechanical orientation treatment is introduced so as to improve critical current density (J.sub.c) of such material to a great extent. The method of the invention is suitable for the production of superconducting products having a specific shape, such as magnets, wires, and the like.
2. Related Art Statement
When made by the regular production process, certain high-temperature superconducting oxide ceramics, for instance, YBa.sub.2 Cu.sub.3 O.sub.7-x type superconducting oxide ceramics, tend to have a comparatively low critical current density (J.sub.c) which is at most several hundred A/cm.sup.2. Such a value for the critical current density is much lower than the theoretical expected level for a single crystal, and considerable improvement is necessary before it becomes ready for practical applications. For example, in the case of wires for superconducting magnets, a critical current density (J.sub.c) of 106 A/cm.sup.2 or more is generally believed to be necessary.
Hence, there is a pressing need for improvement of the critical current density (J.sub.c) by some way or other.
The inventors noted the fact that high-temperature superconductors tend to have crystal grains of anisotropic form, as a reflection of their crystallographic anisotropy. Thus, in order to raise the critical current density (J.sub.c) of high-temperature superconducting ceramics to about the same level as that of a single crystal, it is imperative to homogenize the crystal grain size and to improve the degree of orientation. By increasing the uniformity of the grain size and the degree of orientation, junction areas between grains increase and the packing factor becomes higher. Whereby, the critical current density (J.sub.c) of such high-temperature superconducting ceramics can be improved. The method of the invention uses a mechanical orientation treatment in the production of high-temperature superconducting ceramics material, which treatment includes selection of high-temperature superconducting crystal grains, mechanical vibration, and selection of boundary elements.